The production of superoxide free radicals in pellet and supernatant fractions of glyoxysomes, specialized plant peroxisomes from watermelon (Citruius vulgaris Schrad.) cotyledons, was investigated. Upon inhibition of the endogenous superoxide dismutase, xanthine, and hypoxanthine induced in glyoxysomal supernatants the generation of 02-radicals and this was inhibited by allopurinol. In glyoxysomal pellets, NADH stimulated the generation of superoxide radicals. Superoxide production by purines was due to xanthine oxidase, which was found predominantly in the matrix of glyoxysomes. The generation of 02-radicals in glyoxysomes by endogenous metabolites suggests new active oxygen-related roles for glyoxysomes, and for peroxisomes in general, in cellular metabolism.Glyoxysomes are a class of specialized peroxisomes occurring in oilseeds that contain the fatty acid a-oxidation and glyloxylate cycle enzymes in addition to the characteristic peroxisomal enzymes (17). Recently, we have demonstrated the presence of SOD2 activity (EC 1.15.1.1) in glyoxysomes from watermelon cotyledons (25) and in peroxisomes from pea leaves (9, 26). In watermelon glyoxysomes, two SODs were detected, a preponderant Cu,Zn-containing SOD and, in a minor amount, a Mn-SOD (25), whereas in leaf peroxisomes only a Mn-containing SOD was present (26). Considering that the metalloenzyme superoxide dismutase catalyze the disproportionation of superoxide free radicals (14), the occurrence of SODs in glyoxysomes and leaf peroxisomes strongly suggests that the production of superoxide free radicals takes place in these oxadative cell organelles.In cellular and subcellular systems, the generation of 02-radicals has been demonstrated in neutrophils, monocytes, and macrophages (15), mitochondria (4), chloroplasts (2), microsomes (20), and nuclei (21). However, there is no information regarding the production of oxygen free radicals in purified peroxisomes either of plant or animal origin, and this is important in order to understand the physiological role of superoxide dismutases in cell biology. But, more interestingly, it can contribute to the knowledge of new alternative functions of peroxisomes in cellular metabolism related to activated oxygen species (02 , OH), a field unexplored so far and that could have a potential impact ' Supported by grant 2511/83 C02 from the CAICYT (Spain). 2Abbreviations: SOD, superoxide dismutase; Cu,Zn-SOD, cupro-zinccontaining superoxide dismutase; DETAPAC, diethylenetriaminepentaacetic acid; DMPO, 5,5-dimethyl-1-pyrroline-N-oxide; ESR, electron spin resonance; Mn-SOD, manganese-containing superoxide dismutase; XOD, xanthine oxidase.in multiple areas of cell biology ranging from biomedicine (23, 28) to plant biochemistry (17).In this work, using chemical methods and ESR spin trapping techniques, we describe for the first time the generation of superoxide free radicals by endogenous metabolites in membrane and matrix fractions of glyoxysomes. MATERIALS AND METHODSReagents. Cyt c (type III), DETAPAC, xanthine, hypo...
In peroxisomes isolated from pea leaves (Pisum sativum L.) the production of superoxide free radicals (02-) by xanthine and NADH was investigated. In peroxisomal membranes, 100 micromolar NADH induced the production of 02-radicals. In the soluble fractions of peroxisomes, no generation of 02-radicals was observed by incubation with either NADH or xanthine, although xanthine oxidase was found located predominantly in the matrix of peroxisomes. The failure of xanthine to induce superoxide generation was probably due to the inability to fully suppress the endogenous Mn-superoxide dismutase activity by inhibitors which were inactive against xanthine oxidase. The generation of superoxide radicals in leaf peroxisomes together with the recently described production of these oxygen radicals in glyoxysomes (LM Sandallo, VM Femandez, FL Rup6rez, LA del Rio [1988] Plant Physiol 87: 1-4) suggests that 02-generation could be a common metabolic property of peroxisomes and further supports the existence of active oxygen-related roles for peroxisomes in cellular metabolism.Peroxisomes are subcellular respiratory organelles containing as basic enzymic constituents catalase and, at least, one H202-producing flavin oxidase, and have different metabolic pathways depending upon their origin (15,26). Recently, we have demonstrated the presence of SOD2 activity (EC 1.15.1.1) in peroxisomes from pea leaves (6,22) and in glyoxysomes from watermelon cotyledons (21), a class of specialized peroxisomes occurring in oilseeds. In leaf peroxisomes, a Mn-containing SOD is present (22) and the study of the intraorganellar distribution ofthis metalloenzyme showed that Mn-SOD was located in the peroxisomal matrix as a soluble enzyme (24).
En el momento presente los sectores más informados de la sociedad dirigen su mirada hacia los sistemas de educación y formación con la esperanza de que éstos contribuyan a aportar una respuesta adaptativa a los desafíos del nuevo contexto histórico. Por ello, nunca como ahora la exigencia de acierto, en la definición y la implementación de las políticas educativas, había sido tan perentoria. El presente trabajo plantea la elaboración de un marco analítico para la evaluación de la calidad de la gobernanza educativa, mediante el desarrollo de un sistema de indicadores que reposa en un marco conceptual robusto, previamente definido. Este instrumento de diagnóstico ha sido refinado y validado mediante un procedimiento Delphi de tres rondas sucesivas y se ha estructurado finalmente en 6 dimensiones, 20 subdimensiones y 88 ítems. Un estudio exploratorio de aplicación de la herramienta al caso español ha permitido poner a prueba su fiabilidad. A partir de los resultados empíricos obtenidos del estudio Delphi, se analizan y discuten los criterios de calidad de la gobernanza educativa que han resultado ser más relevantes, y se extraen algunas conclusiones para la mejora de la educación.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.